In the early stages of your relationship, you should ask your boyfriend about his relationship with his family members. Find out how he gets along with them. You'll particularly want to know how he feels about and treats his mother and sisters (if he has some). If he treats them with respect and love and has a genuine appreciation of the characteristics that make them unique, that's a good sign for you. If he displays a rather chauvinistic attitude and you're not into traditional male-female roles, you might do well to run the other way.
When you ask your boyfriend about his family, it is possible that he may answer that he is estranged from one or more of his family members. This doesn't necessarily mean he's a bad guy or a poor catch. It could mean that he was the victim of abuse, either of the physical or verbal variety; it could mean that there were just so many differences that taking some time away from each other was the best thing to do. Watch out, however, if his family relationships are on ice because of his own intolerance. If he becomes upset, angry, or disgusted when a family member doesn't do things the way he expects or wants, you can bet you may be in for the same treatment.
Another important question to ask your boyfriend is how his previous relationships ended and why. You'll want to know what he considers unforgivable in a relationship and what he feels are good reasons to break up. It's a good sign if your boyfriend takes at least a little responsibility for the demise of some of his past relationships, as it's unlikely that he has always done everything exactly right. It's also nice if he has something good to say about at least a couple of his past girlfriends. If he spews hatred about each one, this could indicate an anger issue.
Ask your new boyfriend how you can expect him to act if he is angry or disappointed. Ask him whether he will be forthcoming about what's bothering him or if it's more his style to keep it quiet and bottled up. It's a good idea to encourage him to communicate openly with you concerning his feelings, even when the topic is unpleasant. Good communication can mean the difference between a relationship that lasts and one that goes up in flames rather quickly. If he says anything that indicates that he reacts violently in a relationship, you should strongly reconsider having him for a boyfriend; run the other way.
If you plan to become physically intimate with your boyfriend, ask him about his past sexual relationships. You don't need all the gory details, but you'll want to ask your boyfriend whether he's had a lot of sexual partners and whether he always took precautions to prevent STDs. If he did not always wear a condom in the past, you may want to suggest testing for STDs before you have sex with him. No matter what the result, however, it's important to remember that condom use can give you a good level of safety from STDs, and they are a good idea until you are 100-percent sure that your partner is free of STDs and is, and will remain, in a monogamous relationship with you.
Last but not least, ask your boyfriend meaningful questions about what he likes about you. Of course, it's very nice if he thinks you're beautiful and finds you physically attractive, but you also want to know what he likes about your personality. After all, you want to know that your guy will still like you on one of your most horrendous bad-hair days. You also want to know that he appreciates you for all the little things that make you unique.