It would irritate the crap out of me. My last bf actually looked and answered a text DURING sex. I almost killed him. bf wasnt in a relationship outside of ours but still felt the need to talk to a friend of his DURING! I was so pissed. It ruined the mood lol. IF there is a emergency with a kid etc that warrants a phone call not a text.
It is a respect issue. During your time he shouldnt be talking with his wife about sheets for sure lol. I would be having a discussion with your bf about it. Just because a text comes through doesnt mean it has to be read right then. Thats just my opinion anyway.
She is C He is S