You know he has children, but they are never around. Unless there is a good reason they are not a part of his life, not fulfilling his responsibilities as a father is a warning sign. He may try to blame the situation on their mother or even say the kids just don't want to come over. You might learn that he is way behind on his child support and is making no effort to catch up. If he doesn't take his duties as a parent seriously -- he is likely to shirk other responsibilities.

When you spend time with him and his children, you might find that you and he have different expectations for good behavior. If he lets them rule the roost and doesn't listen to your concerns, probably, their unruliness will escalate. When you try to set boundaries, he might take his kids' side. If you have children of your own, this makes matters even worse. If your relationship has a future, you will have to have consistent rules to avoid a chaotic household.

Watch for signs that his ex uses the kids to manipulate him. If his ex expects him to drop what he is doing to rush over any time a crisis happens -- that's a red flag. While the kids are in his care, she may call constantly or use the kids to spy on what's going on between the two of you. Unless he's willing to set some boundaries, your relationship is going to have a third wheel.

If your boyfriend has unrealistic expectations and often loses his temper with the kids, this is a sign he could become abusive. It's also a concern if you try to step in and he becomes angry with you. If you see unexplained bruises or marks and suspect abuse, immediately file a report with your local law enforcement or child protective services.