Re: How to explain to him that his flirting hurts me?

Start withdrawing that emotional energy-as you might just need to bale out.

He sounds self centered and oafish and not at all considerate.

No-one minds their other half striking up conversations with the opposite sex but it sounds like this chap of yours is pushing it too far. He doesn't sound like he pays you any attention at all when you are in company-and this is just 5 months into your relationship. You should be still in the honeymoon phase. What will he be like in 5 years, 15 or 5o! If you stick around that long.

I would definitely start cooling it-seeing him a bit less often and meanwhile build up a good support base.

Good luck.