My husband broke my heart

My husband and I have been together 12 years. We have 3 wonderful kids together (our youngest is 6). For the last year or so, I could tell things were different between us. Let my preface this by saying that he’s not cheating. I mean, I know there’s ALWAYS a possibility but listen, we both work from home and spend every free moment together or with our kids. I have free access to his phone, I don’t go through it but he just leaves it lying around with no password so the chances of cheating are slim, Maybe that is part of our issue…we are ALWAYS together…there’s no independence. Anyway…he’s been more distant for a little over a year now. He gets frustrated with me much more easily and doesn’t bat an eyelash if I cry (which is rare and he used to do just about anything he could to stop me from crying). Anyway…last night he told me “you know, I don’t see us being together once ****** goes off the college…I just don’t see us making it much longer then they” he was referring to our 6 year old. Now, that’s 12 more years and he’s so sure we won’t stay together beyond that. My heart sank when he said it. I choked back tears and asked him why he felt this way and he shrugged and said “just a feeling I have” and I just got up and walked away. So…yeah…I feel my marriage is over and he’s just waiting til our little guy is college age. I don’t know what to do or how to feel. Any advice or words of encouragement would be appreciated.