It's been a long time coming, and when "Avengers: Age of Ultron" hits theaters at the end of the week, the relationship train will finally come rolling into the station for Black Widow (Scarlett Johansson) and the Hulk (Mark Ruffalo).

He's a giant with a heart of gold, and she's an assassin with a heart of -- well, something. Can these two crazy kids make it work in a romantic relationship? We turned to Terry Klee, a licensed psychotherapist specializing in relationship counseling, to get her professional opinion on whether a great big green guy with anger issues and a trained killer can make magic happen.

In a word: absolutely.

Here's what Klee thinks HulkTasha have going for them:

Opposites attract.

It's an old adage, but so true: sometimes it's our differences that bring us together. Think gentle Bruce Banner can't keep up with fierce Natasha? Think again.

"When you do have an assassin who could kick her boyfriend's ass when he's just the zen dude, he's gentle and has secrets, that's probably his draw to her," Klee said. "We really are drawn to people who pull us out of our comfort zone... So we've got the Black Widow, who's way out there, sexy, takes no prisoners and is independent, and then she's falling in love with a guy who looks like -- by day -- very safe and secure, she likes that, and it's an opposite."

The sex will be great.

Another perk of their opposite nature? Fireworks in the bedroom. "The longer you have the opposite tension, it makes for really great sex," Klee said. "I laugh about that, but sexuality is an important part of any relationship. Couples, one of the first things I'll ask them is how's your sex life. If everything is missionary and they're relaxed and they're safe, they probably by day aren't exciting each other anymore. Whereas you still want to be very interested in the other person's imagination and the things they want to try in life."

Love can sprout in the workplace.

Especially when your work involves traveling around together saving the world over and over again. Rather than dooming their relationship, Bruce and Natasha's coworker status probably helped push them together, Klee said. And it'll help keep them together, too.

"Research shows that proximity and frequency equal a relationship, which is probably why we're always reading in the tabloids about co-stars falling in love," she said. "Some people may say you need separateness and autonomy for a relationship, versus enmeshment. I'd say because of the differences in their personalities, that's already present. Their sense of autonomy and the difference in their personalities, it's already psychodynamically occurring."

The Science Bros. could strengthen HulkTasha's relationship.

As we all know, the bond between Science Bros. Tony and Bruce is very strong. The duo have each other's backs, and tell each other secrets that nobody else on the team knows. Will this BFF-dom drive a wedge between Bruce and Natasha?

It could actually help the couple, Klee said, as long as Tony is a supportive pal.

"When there's three people in a relationship that is most appropriate to be two, it can hinder it," Klee said. "On the other hand, sometimes what occurs and the reason they end up in my office is because they didn't have an Iron Man confidant, so everything is staying inside of them ... You really do have to pour all your LEGOs out on the floor before you can build something. They're all jumbled up inside. The expression that I often use with people is that you can't see your back without a mirror. You just can't. So my role is always just to observe the dynamics and then show someone their back. Iron Man can do that for the Hulk. Iron Man can be quite sensitive. He was with Gwyneth Paltrow at least. He was infuriating to her, also, but he got it."

They'll bring out the best in one another.

"We all kind of have more than one personality inside of us, but we only let one character onstage at a time," Klee said. "For instance, the Black Widow probably has the gentle, zen personality inside her, but she's never really discovered it or nurtured it or allowed it out on the main stage. She needs that part of her. Just like the Hulk, if I psychoanalyze the Hulk, he just gets really pissed off because he's shutting it all down by day. He doesn't know how to let it all out and feel alive. When we let all of our characters out on stage and you're the casting director of all your parts, it's really fabulous and exciting. The daytime Hulk is going to draw out in her a more peaceful side that will let her rest instead of always feeling like she has to keep people away and has no home. And vice versa."

Not even the Hulk's anger issues could keep them apart.

Klee was quick to point out that the Hulk's rage issues aren't so helpful to a relationship, but they can be contextualized with the more humane part of him.

"No one wants to be with an angry partner. This is 2015, you're not allowed to act like the Hulk in a marriage," she said. "To expect the partner to just understand that he doesn't mean what he says is not OK. For the Black Widow to recognize what's going on so she can help the Hulk...[and have] compassion. Meaning, especially say with the Hulk, he really doesn't mean it. He's not a sociopath killer. He's in as much pain as he causes. In a real relationship, everyone is super hurting. People who are enraged, that is a secondary feeling to cover up much deeper pain that they were never able to articulate, which is why the Hulk is so sheepish by day.

They recognize each other's baggage.

The Avengers were clearly shaken after the trauma of the New York battle in "Marvel's The Avengers," not to mention their past life dramas, so the Hulk and the Widow would certainly have to put up with each other's various emotional wounds. And that, Klee said, is what brings a couple together.

"How open you are to the vulnerabilities and quirks and not so attractive sides of another person?" she said. "Whose stuff can you put up with the most is kind of street slang, but very true. For the Widow and the Hulk, we dare to let each other know how complicated and yearning for life we are in different ways, and just have each other's back. You're there for each other. After the really good, hot sex that the Widow is probably going to show him -- he's going to bring out in her what it's like to be human. The Hulk and the Widow, they're very different but not. Not in the endgame."

"Avengers: Age of Ultron" hits theaters May 1.