This isn’t just your problem. It’s a couple problem. You made a mistake. You’ve apologized and you feel terrible about it. You’ve done what you can. Your boyfriend now has to decide if he is going to give you the gift of trust. Yes, a gift. At some point, words of forgiveness have to become action. You apologize. He forgives and renews his trust. You make sure not to betray that trust again.
Meanwhile, he has his own apologizing to do. His mother had no right to make the decision about how you feed your son. If she was concerned, she should have helped you adjust to breast feeding rather than taking action. However, she didn’t “ruin your bonding experience.” You and your boyfriend did. You gave in for the sake of convenience. Your boyfriend didn’t back you up and encourage you to resume breastfeeding. (By the way: Mothers of bottle-fed babies also bond with their babies just fine. Just spend lots of time cuddling.)
You two are a parenting team now. Your boyfriend’s first loyalty should be with you. He needs to apologize. You need to decide if you are going to give him the gift of trusting him to be your parenting partner. He needs to make sure not to betray that trust again.
Meanwhile. What do you mean you have no help with the baby? Real men change diapers, give baths and play with their children. You both made this baby. You both need to be parenting him.
Mutual support with other parents is very important at this stage of your life. If the two of you start taking your baby for long walks at a local park, chances are that you’ll start seeing other young parents. There’s nothing quite like a friendship with someone who has a child the same age. Say hello. Admire the babies. Take it from there. You might also ask your pediatrician if there is a parent support group in your area. Take looking for new friends as seriously as you would look for a job or a partner if you didn’t have one. You deserve the mutual support and sharing that other parents of babies can provide.
I wish you well.