While @Lauren Ipsum's answer is absolutely to the point, I'd like to give you an example: I've also taken up writing a character that is similarly angry, aggressive and generally speaking a jerk.
Then I gave him a love interest, only he didn't realise she was a love interest. For all he knew, she was smart and strong and he decided she belonged to him. Why did she put up with it? A bad case of 'bad guys are sexy syndrome' allied to circumstances that made him the lesser of a few evils.
Up until that point, he hadn't softened the slightest, but since softening him was my objective, I had a kid pop up. I did this because I know of real-life examples where men completely turned their lives and priorities upside-down (for better and for worse) for the sake of their child, and I also researched how things turned out for at least some of those fathers to make sure I wasn't stretching the rope too much.
Facing his own child, his priorities were suddenly rearranged and his sole objective became the well-being of the child. Still no sentimentalities, but he did go back and organise his old life to make sure nothing bad from those times can come and threaten the most important thing in his life.
As the years go by, he discovers that he must at least pretend to get on with the local community for the kid's sake: he needs to know who is who and make sure they're not pedophyles or otherwise accidents waiting to happen. He also needs to be on good terms with parents if the kid is going to be invited to parties. The Love Interest is key here: she gives him the social pointers and, the most important thing, the rewards for keeping up the social front.
Slowly, he starts to have a slight appreciation for a couple of the guys he has to socialise with and, without realising, actually forges some friendships. In the meantime, he comes to fall in love... only he doesn't realise it. He still sees the woman as just being his woman. Sure, he does nice things for her (at first because she would reward him and eventually because it becomes part of the routine... and he does like the rewards), but he still feels love is for suckers and, you know, you can like a woman and not be an in-love asshole.
Basically, I gave him a good reason for him to want to change but he only changed partially. He's still a jerk, by the way, just not as bad and not as aggressive.
Obviously, I'm writing adventure/romance so there's always some action that has him evolve in the right direction. Some of that action also involves facing people and events from his past (the ones he rushed to kick away instead of actually facing and fixing them) which is what makes his aggressive jerk side really get fixed (or as much as possible). But he's never going to be the 'in touch with his feelings' kind of guy. I don't even know if I can realistically make him realise he loves his Love Interest. That aversion to love is just too ingrained in his personality.
What's the point of this all? To stress that your character cannot change quickly. Even if you have a big event force him to re-evaluate his life, you still cannot change abruptly. Just imagine yourself changing your whole way of being in the space of a week: could you do it? And keep at it? No.
The big event can make him want to change (at least a little), but he'll still have to work hard at getting rid of all the bad habits and make a huge effort to create new ones. That's not easy and there are lots of times when you fall back into old habits, which, paradoxically, tend to be more comfortable than the new ones even when you know they're bad for you. Even if he becomes fully aware how wrong his ways have been so far, you still have to break with the bonds of years of acting in a certain way.
Moreover, I don't know much about your character, but I believe that when one decides that emotions are bad for you and then spends an entire life dodging them, even if he has an epiphany and realises he's in love, he's still going to have a hard time acting on that realisation because it means showing emotions. You know, what he spent a lifetime running away from. It's like asking an agoraphobic to go to a busy café daily.