Jealousy in new relationships

Hi will try to keep this brief

I'm 35 years old, father of 3 young girls, who I have custody of after splitting with my wife of 10 years in Feb 2019.
In November '19 I began dating a woman I met online, as I wanted a long distance relationship and could keep my children as my priority.
At the same time I began seeing this person, i became friendly with a mother (who I'll call Charmaine) at my daughters' school, as her eldest daughter was class mates with my middle daughter.
My relationship lasted until march of this year, as the last 2 months of our relationship she was clearly only looking for my money, and the lockdown made our relationship impractical regardless.
I didn't realise Charmaine was interested in me as well. I did suspect when the quarantine started and she began messaging personally, but I assumed she just wanted to keep the girls in touch.
When I told her I'd ended my relationship however, she told me that she'd had feelings for me for months. I was shocked, and over the next couple of weeks we carried on messaging each other and now are in a relationship, despite not actually being able to see each other. She lives on the same street, so we do take the girls to each other's houses so the girls can talk through the window etc, other than that we talk privately at night

The problem is the MINUTE we agreed we wanted to be together, I instantly became insecure. She's 25, smart, and beautiful and I expected a degree of insecurity as I'm that way inclined anyway. But it's worse than I thought, particularly today.
I became angry today that she was slow to reply to my messages (I obviously didn't hassle her I know I'm in the wrong),but for some reason I facebooked stalked her, I suppose. She had changed her profile picture, and I looked into the men who commented, photos with her on nights out etc... I instantly deleted FB, as I don't use it anyway and I do want to be a good partner to her.
I'm not possessive at all, but my instinct is to withhold affection. It's not a punishment, but a way of protecting myself, so it won't hurt as much if she does change her mind about me.
I'm worried that she'll notice tonight that I'm off with her, (I'm so irrationally angry I don't even want her to call) and she hasn't done anything wrong. I don't want to discuss this with her this early on as 1 I'm ashamed and 2 she doesn't deserve any pressure. She admits she's a flirty person but I do want to believe all the nice things she said about me and trust her. I know that will come with time but don't know what to do about it in the meantime

Has anyone been through anything similar? Any advice?