When does married life get boring?

Is that how it is in a marriage? It's boring.

I've been married for 4 years, we have 2 children.
However, we've been together for a little longer (approx. 15 years).
It hasn't been running for about 2 years. It's all so boring. Everyday life has crept in. HE works, I take care of the house and look after the children (I also work for 400 euros on the side).
Somehow the worm is in there. We don't hug, we don't kiss. We sleep together about every 14 days. Always the same program. It's nice and fun, but it usually only takes about 20 minutes, then he's done, turns around and sleeps. We fight a lot. I feel uncomfortable when he's here. Always notice that I'm like a different person when he comes home in the evening. Nothing appeals to me anymore. Find it all so boring. We talked often, but nothing has ever changed.,
It happened the way it had to. I got to know someone else. We have been meeting every now and then for about 3 months. It is nice. We sleep together and it's finally fun again. I don't want any of this, but I can't stop. Now I must have really fallen in love with someone else. I don't even know where my head is. I don't know where to go and what's right.
It's all mixed up right now ...
Yeah, throw stones at me
Who has useful tips?