Look at other people's tattoos for inspiration. If you see a person with a text tattoo you particularly like, make a quick sketch of it or take a photograph - with their permission, of course. Similarly, if you see a tattoo you don't like, take note of what it is about the piece that turns you off. Rather than photographing a tattoo you don't like, it might be better to make a sketch or take notes of what you didn't like in a notebook. Research such as this will help you avoid making the same mistake yourself.
Study websites that feature fonts and books filled with styles of fonts to choose a lettering style you like. Consider that the simpler and bolder the font, the easier it will be to read your "I love my boyfriend" tattoo.
Use the fonts on your computer to type the words "I love my boyfriend" again and again and print out the text at roughly the size you want your tattoo to be.
Hold the printed text against your skin on different parts of your body to determine the best placement for your tattoo. Better yet, have an artistic friend write the text on your skin with a marker in a similar font so you can see how it will look as you move around.
Visit as many tattoo shops and view the work of as many artists as possible. View artists' portfolios, paying particular attention to their text tattoos. Keep in mind you can also ask the artist to add a design to accompany the text. The artwork can be representative of your relationship or simply something you find attractive. Interview artists to make sure you find them friendly and knowledgeable enough so you're completely comfortable before you allow them to execute your "I love my boyfriend" tattoo.