There's a large facebook group of female runners who tend to classify their partners as CW (cockwomble) or NCW (non-cockwomble) to various degrees, this terminology is solely about whether their partner supports their running. So it's not unusual to have a partner who doesn't get it about what a big achievement PBs etc are.
If the relationship is otherwise good, and he doesn't put you down about it, then I'd simply seek the encouragement you need from fitness friends (either in person by joining a running group, or online). Sometimes we expect our partners to be everything to us, but we can get better support for aspects of our lives/hobbies from other people who share those interests.
However, some of the things you have said go beyond him being disinterested in your new hobby. They sound really mean and spiteful. He shouldn't really be cutting you down like that and trying to undermine your confidence in your changing body and fitness levels. He sounds like an insecure bully, and I wonder whether he's emotionally abusive in other ways.
I took up running this summer and I'm a new convert to exercise who was (and still am to a lesser extent) obese. I know the zeal of discovering fitness and actually enjoying it, and I also have a lifetime of previous disinterest in exercise. So I can see both the 'wow, you are doing awesome' and the 'so boring' thing. My DH has been supportive of me becoming fitter and healthier, though isn't rivetted by the details of workouts nor keen to have a go himself. He absolutely hasn't bullied me about changes to my body though. He wants me to be fit and healthy and knows that part of why I want to do that is for our family and future family.
There's two things you need to consider:
- Are there other ways in which he is emotionally abusive?
- How does he react to you saying that the comments he makes are hurtful, unsupportive and you want him to stop?
You have made amazing changes to your life, I know how hard it has been for me (and I've got a long way to go) but you've done that without the support I've had, on your own. It is a huge achievement, don't let him diminish it or you.