Rude boyfriend after a night out

My boyfriend and I get along fine and well, had some hiccups in the past but now everything is okay...

Except after he’s been on a night out!! He doesn’t go out often, maybe once a month or so. But when he does he doesn’t text me the whole time he’s out and the following day he either doesn’t text me for ages or is just incredibly rude to me. This usually happens when he goes out with his brother who I feel is a very bad influence on him.

For example, last night we were both on separate nights out, me with a friend and him on a bachelor party/stag do, and we were supposed to meet up at the end of our nights to go back to his... from 5pm last night until 11am this morning I didn’t get so much as a text back (despite having “read” my messages) - but then I find out through his brothers snapchat story he left the bachelor party to go meet his brother in a club. So in essence he couldn’t text me back to let me know what was going on - not even to let me know he was longer meeting me as planned - but he was perfectly capable of messaging his brother to meet up with him.

When his brother is involved I am no longer a priority at all, I am dismissed and ignored. His brother ended up staying back at his and I had to text his brother this morning just to get him to tell my boyfriend to message me back! And when he did message me he was so short and rude and then ended up ignoring me again until later on in the evening! I’m baffled.

Like I said, we get on great usually but it’s when he is out particularly with his brother that he is really disrespectful to me. Everytime I try to speak to him about it he just dismisses me. We have been together for over two years and this has been an issue on and off for the entire time.

Advice please :(