Summarize:

When you begin having the conversation, phrasing is very important. It's easy to accidentally come off like you're blaming or judging the other person. Proper phrasing can help the conversation go smoother. Avoid statements that start with "you" as this comes off as you forcing external judgment on the situation. Instead, phrase everything in terms of "I" and tie it back in to how your feelings affect your ability to function in the relationship. For example, instead of saying "You don't let me spend weekends just with my friends," say something like, "I like to sometimes just go out with friends Friday nights, and if I was able to do that more often I'd be happier when I came home to you." Avoid harsh language in general. Words like "clingy" or "needy" can come off as judgmental. If you feel your boyfriend wants too much of your time, instead say something like, "I feel like it's hard to meet all your needs all the time, and I don't have energy for myself when we spend all our time together." Be transparent. Talk about what you discovered while reflecting on the relationship and yourself during your talk. Saying you need space can potentially make your boyfriend feel very insecure, so focus on how the issue is about you and your needs and has nothing to do with how you feel about him. A relationship is a two way street. If your boyfriend has different ideas of what constitutes healthy space than you, the two of you need to address this together. You should listen to how he responds to what you're saying. Your boyfriend's needs and desires are as valuable as your own, so treat them as such. Remember this as you have the conversation. This is not an issue of one party being right and the other being wrong. It's an issue of differing personal boundaries. If you don't understand, ask for clarification. Something like, "Why do you feel that way?" can really help you better understand your partner's needs. At the end of the talk, reinforce your enthusiasm for the relationship so things do not end on a bad note. Say something like, "Even though I need alone time on occasion, I really do love spending time with you and want to be with you." It's a good idea to, throughout the talk, throw in positive statements and sentiments. Like, if you discuss spending more nights at your own place, follow up with something like, "Even though I really do love waking up next to you in the morning." This can help the conversation sting less for your boyfriend.
Use your language carefully. Listen to your boyfriend's needs as well. Reinforce the positive.