All the people I know who are in happy relationships make time everyday to be alone bonding with their partner. Whether its doing a house project together or cuddling on the couch after the kids are asleep. Its important. It needs to keep being reciprocal.

I dont mind if they have friends of the opposite sex they keep in contact with just so long as they are committed and actively engaging in their relationship with you so that there is trust. However,when their friends drama becomes more valuable than your own it crosses the line. At that point it feels like the other partner has just given up on the relationship.

Maintaining relationships with past lovers is also another red flag. The eating at two tables thing. Unless they have a kid and the relationship is figuring out when visitation and holiday things will be going on. Its a sign that they have an attachment issue with the ex and are not over them and ready to move into a genuine relationship with you. That baggage will prevent the nurturing of your relationship with them. I've experienced that first hand.

Above all those i know that are in strong healthy relationships have a sense of mutual teamwork. They both support each other and move towards a common goal. They truly are partners. The relationship is on the rocks when once side stops giving a crap or extending themselves anymore.