Personally, i think it's a little unfair to say you, for example, don't want kids, while you are dating, and then flip the script once you get married and say you do. You were already 30 yrs old when you married him and should have known that.
Not scolding you but just saying maybe you need to take one for the team on the issue of having kids.
But no, you should not accept him turning into a couch potato.
Get some hobbies, nurture some (female) friendships and try to have some fun in your marriage.
My exhusband is almost 12 years older than I am and it was not a fun experience. We were at very different places in our lives and really wanted and needed different things.
Sure, you can leave him for a younger man. But I dn't think that is the answer. At least try to make some changes with him.
Can you sign up together for a cooking, dancing, massage, whatever class? Or find two other couples and plan a monthly night out thing? Maybe sign up for Big Sisters and mentor some girls? Or volunteer at church or for a dog rescue or some other cause that is close to your heart so you feel needed and validated in some way (besides motherhood)?
Your situation def sounds frustrating. Just don't let yourself get so lonely you do something stupid.