Whether you and your boyfriend stay together as is or end up getting married, it would be more peaceful if everyone was on good terms. If you catch one of them alone you could broach the situation by saying something like we used to be closer but I feel a distance now. Did something happen. If you have to choose between writing them off versus going the extra mile for peaceful relationships I think long term the latter would be better. It doesn't matter who takes the first step. Best wishes.