I saw two of the mum's from my local baby group take their babies out together on fb and they didn't invite me or my little one along so I saw red and just unfriended them both.
And how did you feel once you had done that?
Are you happy to have done it, or do you feel it was a disproportionate reaction?
Other people are allowed to meet up without you. If you want to meet up with other mums, don't passively wait for an invitation - make one yourself. Be prepared for other people to be busy, to not accept every invitation, & the fact that they will also be meeting other friends & acquaintances.
You have cut off your nose to spite your face by unfriending these 2 mums. Life can be hard, & unfair, & until you find a way of becoming more accepting of that, you are going to constantly measure your own happiness & self-worth against what you think other people have.
I feel jealous of their relationships with their baby dad's, their friendships with other mums and their homes, cars ANYTHING even though I'm better off than a lot of them?
You can cure yourself of 'baby dad' jealously with a quick browse of the Relationships board here. Living with a man isn't always the golden ticket it's sold as - there are plenty of women presenting a good face to the world, but being dominated, undermined, neglected, cheated on ... whatever ... who would LOVE to be single & independent like you.
As to the cars & homes - so what? As you say yourself, you are better off than many of these mums. You will be worse off than others. This is the way of the world, & if you keep taking it personally, you will destroy your own happiness.
I think you need to spend some time - a LOT of time - working out where this jealousy comes from. Because it sounds more like a symptom than a disease. What is going on with you that you look at other people's lives & imagine that they are somehow 'better' than yours?
The best thing you can do for yourself is find a therapist you feel comfortable opening up to - really opening up, all the hidden & uncomfortable parts of your psyche - & start to establish the real root cause of your jealous inclinations. Only then will you be able to understand & deal with these uncomfortable emotions. You need to work through why you are making yourself unhappy with shallow comparisons, & find out what makes you tick, what gives you contentment, & how to develop pride in your own achievements.
Behaving like a thwarted toddler & unfriending acquaintances on facebook for the 'crime' of meeting each other is a devastatingly self-defeating act.
I've tried just being happy for people but I'm not.
When you are happier in yourself, that will come naturally.
Get some professional help about why, instead of creating the life & relationships you want for yourself, you are bitterly assessing other people's lives & blighting your own by viewing it through a negative lens of constant comparison.
You're not going to change this aspect of yourself overnight. It will be a series of small steps, but you can enjoy the learning process & benefit from finding out more about how to manage yourself & these horrible feelings of jealousy. Commit to finding a good therapist today, & take that first step! 