He responded to a females story inappropriately

So my significant other and I have been together for about 5 months now.. today I went into work today and my coworker pulls me aside to ask if we are still a thing, she then proceeded to tell me he responded to her photo on snap chat saying something very inappropriate. After she told me she showed me and it was indeed VERY inappropriate, so I don’t know what to do idk if leaving is to dramatic or what. I’ve been in a bad relationship before this that created trust issues, but I truly trusted my current partner and never thought he would do anything in that form. He says he’s sorry and he was drunk but from my past I’ve learned if they do something once it will continue! So any advice?