First, thank you for this site and your willingness to answer some tough questions in a biblical manner. I don't know how to ask this without seeming to be lustful, but I want to be honest. Is it wrong for a male to consider or even enjoy certain physical characteristics (i.e. large breasts) of a woman they are dating and plan to marry? I know that it is wrong (not to mention downright stupid) to consider this only when choosing someone, but if you both are God-fearing and evenly yoked in all other areas, is this wrong? Is this considered a 'fetish'? Thank you in advance for an honest and scriptural answer!
Physical features are frequently what gets one person to notice another. Most often men notice physical characteristics because they are visually oriented. But it isn't the size of the breasts, what you find most often is that boys have a tendency to pick girls who have some physical characteristics similar to their mothers. People tend to find comfort in the familiar. It isn't even close to a hard-fast rule, but there is definitely a trend.
But I'm glad that you realize that physical features are not what should enter your decision of whether to marry someone. Physical features change as a person ages. Accident and disease might cause loss of a particularly attractive feature. For instance, if you expressed to your wife that what particularly caused you to want to marry her was her breasts, then what happens if she gets breast cancer? Is she going to avoid the needed surgery because she is concerned that you won't love her anymore?
Telling a woman that you appreciate her beauty is one thing, but to indicate or even hint that you wouldn't have married her if she didn't have that particular feature is something else entirely.
If you read the first three chapters of the Song of Solomon, you find Solomon complementing the heroine many times about her overall beauty and some "safe" specific features, such as her complexion, but he does not mention specific and more intimate features until after marriage. To dwell on such features before marriage is to arouse too much sexual interest at a time when it cannot be expressed. I am assuming when you say you are enjoying your girlfriend's breasts, that you mean you find her overall look pleasing and not that you are touching this intimate area of a woman's body or getting yourself sexually excited over them.
According to the dictionary, a fetish is a charm, amulet, pendant or other decoration associated with magical properties; it often represents an animal or person. It creeps into our society because people used to wear "magic" charms in hopes of creating sexual interest. Thus, today, a fetish is often a sexual fixation on a concept, object, or body part. A person with a fetish feels a compulsive need to use the object in order to obtain sexual gratification, and cannot achieve pleasure without it. I'm bringing this up because I very much doubt, and very much hope, that this is not how you are treating the girls you have dated.
What should be critical in your selection of a person to date and eventually marry is their character because character rarely changes. But character is harder to figure out and to get to know. A glance might tell you about someone's physical features, but it takes time to find out how a person reacts and makes decisions in various situations.
After marriage, it is right and proper to enjoy all aspects of your companion. "Drink water from your own cistern, and running water from your own well. Should your fountains be dispersed abroad, streams of water in the streets? Let them be only your own, and not for strangers with you. Let your fountain be blessed, and rejoice with the wife of your youth. As a loving deer and a graceful doe, let her breasts satisfy you at all times; and always be enraptured with her love. For why should you, my son, be enraptured by an immoral woman, and be embraced in the arms of a seductress?" (Proverbs 5:15-20).