At only 22, you’ve already lived a lot of life. The death of a child is devastating. I’m very, very sorry for your loss.
I’m wondering if your unhappiness with your partner is related. People grieve differently. It may be that you and your partner have handled the loss so differently that you have lost sight of each other. You are busy with a toddler all day, which can be a major distraction from your feelings about your son. Your partner may have thrown himself into work or outside activities as a way to manage his feelings. Such differences will inevitably lead to partners feeling distant from each other.
You say your partner doesn’t make you happy. He can’t. No one can make another person happy. What you can do is support each other so you each find happiness in yourselves and in your relationship. Incomplete grieving and your inability to talk about it with each other are likely part of what is getting in the way.
In addition, I’m going to guess that you have the same feelings as many young mothers. Many, many mothers tell me that they are exhausted by the constant demands of little children. Their sex drive goes down. They wonder who they are apart from being a mom. Meanwhile, many, many young fathers tell me that they feel left out; that they don’t know how to fit in with the intense bond between mother and child. Not having a clue how to raise the subject without sounding like they are whining, they distance from mother and child, focusing on making a living to support the family.
i’m not at all sure that “breaking up’ with your partner is an answer. Before you make such a drastic decision, I hope you will talk to him about seeing a couples counselor together to help you both deal with the loss of your son and to help you become a family of three, with everyone’s needs getting met. Do bear in mind that because you have a child together, you can never completely walk away from each other. If you find you really can’t reignite the spark between you with the counselor’s help, then focus on how you are going to manage being effective co-parents for your little girl. She deserves to have the love and care of both her parents.
Please give counseling a chance. There is much more going on here than incompatibility. Your daughter deserves to have both parents in her life as much as possible. You and your partner deserve to deal with all that has happened over the last few years in a way that makes it possible for you to be fully in a relationship (even if it isn’t this one).
I wish you well.