When my girlfriend and I for the first time did a threesome together with her former boyfriend it was an absolutly normal thing to me to also suck her former boyfriend's cock and my girlfriend was totally fine with that. That was the start of a very close friendship between us and him and every time we meet for a threesome her former boyfriend and I sucked each other's cock and sometimes we jerked each other off. My girlfriend was totally happy about our close friendship bacause she loved having sex with him so very much.