I've been through TT regression with 2 of my kids. The best thing you can do is to forget about it for a while and try later maybe a month or two. There is no point in fighting with him or getting upset as it will probably make it worse between you. I begged, cried and bribed for weeks and created tension between my DS2 and I that didn't need to be there. When my DD regressed for a while not long ago after TTing before Xmas and when I found myself getting frustrated with her, I put her back in nappies. I asked if she wanted to use the potty if I saw her acting like she needed to go but I didn't push the issue. It lasted a few weeks before she started telling me she needed to go again

I have to add too that it can be a control issue. ie this is the ONE thing that he has control over you with. Once you show him that you "don't care" then he might lose interest in trying to control you with it.